long while, the hygrometer never attained a point higher than 93. In the same experiment under the receiver inverted over water, Mr. Ronalds found the number of strikings gradually to decrease, from 4.5 in a minute even to no striking. I am not surprised at this effect, as it proceeds from the cause which I have already indicated; for the glass tube in which the column was inclosed being more and more covered with moisture, its surface was at last become such a conductor of the electric fluid from the positive to the negative end, that it became neutral.

The last experiments of Mr. Ronalds would have surely reconciled our opinions on this subject, had they been made on purpose for its investigation; being made with a column similar to mine, composed of 800 groups, supported between three glass pillars covered with sealing-wax; but these experiments were made for a different purpose. He placed an hygrometer, a thermometer, and an electrometer under a receiver inverted over mercury, in order to introduce successively an acid and an alkali, and to observe the degree of dryness they would produce: with the acid the hygrometer descended from 46 to 29 by the temperature 591; having then removed the acid and substituted potash, in the course of a day it brought the hygrometer to 24.

These experiments, and the following, in which Mr. Ronalds made moisture increase under the receiver by introducing in it a moistened card, were made with the view of trying the effect of more or less moisture for increasing the action of the column, shown by the number of strikings of the gold leaf in the electrometer, in a given time, compared with the effects of the changes of heat: they certainly prove that the increase of heat accelerates the strikings, as Mr. Singer had supposed; but they show at the same time, what small quantity of evaporated water in a given space, produces in it extreme moisture, and that the increase of heat with the same quantity of water, tends to diminish moisture.

This I know by my own experiments, which are the object of my paper in vol. xxxiii of Mr. Nicholson's Philosophical Journal, giving an account of two series of experiments, agreeing with each other, by which I determine the number of grains of water which can remain in the state of vapour in the space of one cubic foot, by each degree of my hygrometer and of the thermometer. It may be seen in the table of the results, that seven grains of water evaporated in one cubic foot, by the temperature of 60, brought the hygrometer to 96.6 degrees, and that then the smallest diminution of heat caused a deposit of water on the sides of the vessel. This shows what small quantities of evaporated water act on the hygrometer in all its degrees; an important circumstance to be attended to in meteorological systems; a subject to which I shall return.

The above experiments made with the greatest care in a glass vessel, which was air-tight, show that such experiments made under a receiver are more difficult than is commonly imagined, and that they cannot be opposed to my experiments made in open air, which de

monstrate that the action of the column is increased by the increase of moisture, and diminished by dryness. But a more direct proof of it is related in the same Philosophical Journal of Mr. Nicholson, for August, 1810, by some experiments which I have made with my late very ingenious friend Dr. Lind, for ascertaining immediately the influence of moisture on the action of the column.

In this experiment all the parts of a column were first separately laid on the hearth of a chimney before a great fire, so that the pieces of paper were almost singed. In that state we mounted the column, and it did not affect the gold leaf electrometer. We then dismounted again that column, and laid also the separate pieces on a table in my room, in which the hygrometer was about 40°. When they had thus remained one hour, we remounted the column, and it acted on the gold leaves as it did before the papers had been so thoroughly dried by a great heat.

This I think to be a direct fact proving that a certain degree of moisture in the column is indispensable for its conductive faculty, the source of all its effects. I have found in all my observations, that within certain limits an increase of moisture increases the action of the column; but, whereas the effect of the increase of heat is immediately perceived, as it easily penetrates the column, that of the increase of moisture is very slow, because, beginning at the edge of the papers on the outside, it very slowly propagates in the internal parts of the column; a circumstance of which Mr. Ronalds has not been aware, especially by his column being inclosed in a glass tube.

But the column being a very new apparatus, it requires some time and a greater number of observers to follow all the views it opens in the terrestial phenomena, especially in those of the atmosphere which constitute meteorology. This was my general conclusion in a paper published in vol. xxxiii of Mr. Nicholson's Philosophical Journal, under this title: "On Hygrology and Hygrometry, and their Connexion with the Phenomena observed in the Atmosphere." There I demonstrated that important fact, not only in meteorology, but in natural philosophy, that rain does not proceed from a quantity of aqueous vapour or moisture existing at any time in any portion of the atmosphere; that it must proceed from the decomposition of the atmospheric air itself, from which decomposition more or less complete result all the meteors, lightnings, thunder, hail, and other atmospheric appearances.

I have been thus particular in the examination of Mr. Ronalds's opinions, as he has shown much ingenuity in his experiments, and because, having had the opportunity of being personally acquainted with him, I agree with the judgment of Mr. Singer, in the opening of the same paper, that Mr. Ronald's "is an electrician of great promise, and whose scrupulous attention to the essentials of accurate experimental inquiry has afforded me pleasure to observe." I am, sir, your most obedient servant, J. A. DE Luc.

Windsor, September, 1814.

Experiments on the Variable Action of the Electric Column. By FRANCIS RONALDS, Esq., Communicated by Mr. SINGER.*

VERY soon after I had constructed a pendulum apparatus similar in principle to that of M. de Luc, described in vol. xxvii, page 161 of Nicholson's Journal, and had observed the variety of its action, I suspended an hygrometer and a thermometer near it, by which I found that when the latter rose but one degree, a difference of four to five vibrations in a minute took place, whilst no such effect occurred if the former advanced two or three degrees towards dryness unaccompanied by a corresponding rise of the thermometer. It was therefore evident that heat is the principal cause of the variable action of the electric column.

The following experiments were made with a gold-leaf electrometer, in order that they might be repeated and varied by any one who may not be inclined to construct the pendulum apparatus of M. de Luc's contrivance, or provide himself with one.

The negative end of a column consisting of 1000 groups of zinc and gold paper, enclosed in a glass tube with interposed discs of paper, as improved by Mr. Singer, was screwed upon one side of a brass tripod, an electrometer on another side, and an hygrometer and thermometer on the third side. A glass dish was placed under the tripod, and the whole apparatus arranged upon the plate of an air pump.

An observation was generally made every five minutes. In the third experiment the mean of several observations is set down instead of each for the sake of brevity. The first column gives the time; the second the degree of the hygrometer; the third that of the thermometer; and the fourth gives the number of strikings per minute of the gold leaves.

Experiment 1. Was destined to try whether at equal degrees of heat and moisture in the open air an uniform action prevailed, and the result shows that it was nearly so.

Exp. 2. Shows that the same uniformity continued in the receiver, which was not air tight.

Exp. 2. Shows that when the air of the receiver was gradually heated from 53 to 70, and by this means the hygrometer made to advance 9 degrees towards dryness, the electrometer increased its strikings progressively from 3.75 to 17 times per minute.

Exp. 4. Proves that the column had not undergone a permanent change by experiment 3.

Exp. 5. Shows that when the air of the receiver was dried by means of sulphuric acid from 37 to 61, giving for the whole diminution of moisture 30 degrees, no increased intensity took place.

Exp. 6. Proves that the column had not been permanently affected by the last experiment.

Exp. 7. Shows that when the air was moistened 56 degrees, the intensity was diminished from 44 strikings per minute to a divergence of 6 inch.

It would be unnecessary and tedious to detail some other experiments which were made with a different view, but which conspired with the above to indicate that heat is the principal cause of the phenomenon, and that a moist atmosphere produces exactly the same effect on the glass tube of the column that it does on the insulators in all other electrical experiments.

It now therefore seems a matter of some interest to resolve several queries relative to the mode in which heat acts: for instance, does it promote the electromotive powers of the metals? Does it produce the effect by giving motion to the combined moisture of the interposed discs of paper, or by rendering those discs more or less conducting? Is there any analogy between the column and the tourmalin? The justly celebrated inventor of this modification of the Voltaic pile, having first observed that equal degrees of heat and moisture were not accompanied at different times with a corresponding intensity of action, conceived that this difference was occasioned by changes in the electrical state of the ambient air, for which reason he gave it the name of Aërial Electroscope, and I think the evidence of our present experience preponderates in favour of the conjecture.